import java.util.HashMap;
import java.util.Map;

class Solution {
    public int minNumberOfFrogs(String croakOfFrogs) {
        char[] ret = croakOfFrogs.toCharArray();
        String ss = "croak";
        int n = ss.length();

        int[] hash = new int[n];
        Map<Character,Integer> index = new HashMap<>();

        for(int i = 0;i < n;i++)
            index.put(ss.charAt(i),i);

        for(char ch : ret) {
            if(ch == ss.charAt(0)) {
                if(hash[n - 1] != 0) hash[n - 1]--;
                hash[0]++;
            }else {
                int i = index.get(ch);
                if(hash[i - 1] == 0) return -1;
                hash[i - 1]--; hash[i]++;
            }
        }

        for(int i = 0;i < n - 1;i++)
            if(hash[i] != 0) return -1;

        return hash[n - 1];

    }
}